The present invention relates to a simulation method which analyzes air flow around a golf ball having on a surface thereof at least one depression or protrusion when the golf ball rotates while in flight. More specifically, the invention relates to a simulation method for evaluating golf ball performance, which method sets up a golf ball model and air flow on a computer, employs arithmetic operations executed by the computer to analyze air flow around the golf ball, and calculates a lift coefficient and a drag coefficient for the golf ball.
It is known that when a physical body such as a golf ball flies through the atmosphere, airflow turbulence arises around the body. If the surface of the body has a complex shape or the body rotates while in flight, the airflow turbulence during flight is complex and exerts a major influence on the flight performance of the body, such as the flight distance.
Golf balls are usually provided with a large number of dimples of circular shape, as seen in a plan view. Because the combination of dimple parameters such as three-dimensional shape, arrangement and size has a major influence on the aerodynamic properties of the golf ball, it is necessary to understand the causal relationship between these dimple parameters and the aerodynamic properties.
Generally, when investigating the effects that changes in dimple parameters such as shape, construction and arrangement have on the flight performance of a golf ball, it has commonly been the practice to fabricate a variety of molds for molding golf balls and test-produce various golf balls. The balls are then subjected to ball striking tests and properties such as the initial velocity, spin rate and trajectory (flight distance, height) are measured, from which the aerodynamic properties are evaluated.
However, such experimental evaluation based on actual physical prototypes is time-consuming and costly, and moreover cannot clearly establish causal relationships between the shapes and arrangement of the dimples and the aerodynamic properties of the ball. For this reason, golf balls which have been newly designed based on evaluation results obtained by experimentation often fail to achieve the intended performance. In such cases, it is necessary each time to design and produce a new ball prototype and determine its aerodynamic properties, generating a further outlay of time and expense, and thus making efficient golf ball development impossible.
To address this problem, the inventors earlier proposed a simulation method which sets up, in a computer, a golf ball model and a virtual airflow space surrounding the periphery of the golf ball model, establishes a state where an air stream flows into the virtual airflow space, calculates the coefficient of lift and the coefficient of drag for the golf ball and, based on these calculated values, estimates the trajectory of the golf ball when it is hit (JP-A 2006-275722; U.S. Pat. No. 7,435,089).
However, evaluating the performance of a golf ball by this simulation method takes a very long time, and actual evaluation is not always feasible. That is, in this simulation method, to calculate the coefficient of lift and the coefficient of drag, a grid is generated within the virtual airflow space, the grid being set up so as to be finer near the surface of the golf ball model and to become larger at an increasing distance from the surface. The velocity, direction and pressure of the air stream are calculated for each cell of the grid and integrated, thereby calculating the coefficient of lift and the coefficient of drag. However, calculating the coefficients of lift and drag takes a long time and, because the trajectory of the ball is estimated by repeating these calculations as the ball moves, simulating the trajectory in this way ends up taking an inordinate amount of time.
Prior-art literature other than that mentioned above (JP-A 2006-275722, U.S. Pat. No. 7,435,089) relevant to the present invention is shown below.
JP-A 2002-358473
JP-A 2005-034378
JP-A 2002-340735
JP-A 2002-250739